1. Field of the Invention
The invention relates to the grinding or regrinding of tools used for thread cutting or similar forming tools, in which it is desired to form both a thread cutting angle and a compound relief angle on the tool.
2. Description of the Prior Art
In the past, it has been necessary to either grind the cutting edge and the relief or rake angle as successive operations, or provide complicated tools, jigs, or fixtures for grinding both the cutting and relief angles simultaneously. One known construction involves a double angle or compound vise which is shifted in one plane and then in another plane to get the double angle required for the tool with respect to the grinding wheel. A problem with this old construction is that the second shifting operation alters the first angle and therefore the settings must be repeated until they are accurate. It is often necessary to check the tool position with a comparator such as one which compares the tool position with a greatly enlarged drawing. This is a very time consuming operation but is necessary since thread cutting tools must be extremely accurately machined.
Other known constructions and methods include jigs or fixtures having compound angles formed on them and other devices which combine angular surfaces with rotatable bushings in which the tool is mounted. These prior devices have been found unsatisfactory for a number of reasons including their complex nature and cost of manufacture. There is in existence a double angle vise which, when the tool is moved in one plane, automatically compensates for the angle in the other plane, but this is also a very expensive construction.
Among the patents representative of these prior constructions are the following:
______________________________________ Inventor U.S. Pat. No. ______________________________________ Wilson 2,385,902 Benjamin et al 3,065,580 Sherman 2,912,801 Landy 2,317,996 Jorgensen 1,908,155 Heineman 2,730,846 Grieco 2,448,309 ______________________________________
In Wilson U.S. Pat. No. 2,385,902, for example, each pair of surfaces A and B on the fixture are related to each other by a compound angle and it would be very difficult and expensive to manufacture a fixture of this type.
It is known in the field of miller cutter grinding to position a grinding wheel axis in the plane of a cutting edge, retract the grinding wheel from the cutting edge a distance proportional to the relief angle desired, plunge ghe grinding wheel towards the miller cutter and grind the cutter edge. However, the problem of compound angles does not exist in the field of grinding miller cutters and the present invention adapts and varies this known method and combines it with a novel jig construction to achieve the improved results described in this application.